Methyl silicone grease composition and method of making same

ABSTRACT

A grease composition contains a polysiloxane, the organic substituents of which are methyl radicals, a higher fatty acid soap of lithium, an amount of a polyether which is sufficient to cause the lithium soap of the fatty acid to disperse into the polysiloxane, but insufficient to deleteriously affect the hightemperature properties of the grease, and a sufficient amount of a base to render the grease alkaline. The grease is made by heating together the polysiloxane, the polyether, the lithium soap of the higher fatty acid and the base to a temperature of about 400* to 500* F., after which the grease composition is cooled to room temperature, then milled. The grease composition is used in the journal bearings of starter motors having highcurrent capacity and which run hot but are subjected to extremely low temperatures when not running.

United States Patent Inventors John B. Wright Elnora; Abraham L. Hajjar,Schenectady, both of N.Y.

App]. No. 762,346

Filed Sept. 16,1968

Patented Nov. 16, 1971 Assignee General Electric Company METHYL SILICONEGREASE COMPOSITION AND METHOD OF MAKING SAME 4 Claims, No Drawings US.Cl 252/42.l, 252/49.6 int. Cl Cl0m 7/50, ClOm 7/20 Field of Search252/42. 1, 49.6, 52 A References Cited UNITED STATES PATENTS 6/ i954Hotten et al. H 1

2,684,944 7/1954 Zajac ABSTRACT: A grease composition contains apolysiloxane, the organic substituents of which are methyl radicals, ahigher fatty acid soap of iithium, an amount of a polyether which issufficient to cause the lithium soap of the fatty acid to disperse intothe polysiloxane, but insufficient to deleteriously afiect thehigh-temperature properties of the grease, and a sufficient amount of abase to render the grease alkaline. The grease is made by heatingtogether the polysiloxane, the polyether, the lithium soap of the higherfatty acid and the base to a temperature of about 400 to 500 F afterwhich the grease composition is cooled to room temperature, then milled.The grease composition is used in the joumai bearings of starter motorshaving high-current capacity and which run hot but are subjected toextremely low temperatures when not running.

METHYL SILICONE GREASE COMPOSITION AND METHOD OF MAKING SAME Thisinvention relates to improved methylpolysiloxane grease compositions andan improved process for making the same. More particularly, the presentinvention is concerned with organopolysiloxane grease compositions, theorganic substituents of which are all methyl, and a method for makingthe same which eliminates the formation of soap lumps in the finishedgrease.

organopolysiloxane greases and grease compositions are well known in theart and have been used as lubricants, dielectric compounds, sealingcompounds and high-vacuum greases. These organopolysiloxane greases havebeen particularly valuable because of their high degree of heatstability, their water repellency, their lowand high-temperatureviscosity characteristics and dielectric properties.

In the past it has been extremely difficult to prepare greasescontaining a silicone fluid all of the substituents of which are methylin combination with a higher fatty acid soap by means of a melt process.The soap and the silicone fluid are incompatible because the soap andthe silicone fluid are incompatible because the soap does not absorb thefluid and soap lumps are formed in the grease. This interferes with themechanical processing of the grease and results in a final product whichhas poor bleed characteristics and poor stability at higher temperaturesand during storage.

To solve this problem of lump formation in silicone greases, it has beenfound that long chain alkyl groups and aryl radicals could be used toreplace the methyl radicals on the polysiloxane and thus give bettercompatibility with metal soaps of higher fatty acids. The proposedtheoretical reason for the compatibility is that the large organicradicals on the polysiloxanes are adsorbed on or dissolved in the longalkyl groups on the fatty acid soap. While the substitution of higheralkyl radicals and aromatic radicals for the methyl radicals on thepolysiloxane used to make greases have served their purpose so far ascompatibility is concerned, some of the radicals added have had anadverse affect on the desirable characteristics, particularly thethermal breakdown characteristics of the organopolysiloxane component ofthe grease composition. Other radicals have resulted in goodhigh-temperature lubricating properties at the sacrifice oflow-temperature propertics.

It is an object of the present invention to provide improvedorganopolysiloxane grease compositions which retain most of thebeneficial properties of heretofore known polysiloxane greasecompositions and which, in addition, are easy to make and inexpensive.

This and other objects of my invention are accomplished by an improvedmethylpolysiloxane grease composition containing a minor amount of apolyether. It has been found that the presence of a minor amount of apolyether in a methylpolysiloxane grease composition containing alithium soap of a higher fatty acid provides markedly improvedcompatibility between the lithium soap of a higher fatty acid and thepolysiloxane component. This prevents the formation of largeagglomerates of soap during the manufacturing of the grease and allowsthe preparation of a grease with desirable properties. The greasecompositions of the present invention consist essentially of, on aweight basis:

1. from 61 to 98 percent of a polysiloxane fluid, the organicsubstituents of which are methyl groups;

2. from 2 to 35 percent of a lithium soap of a higher fatty acid havingfrom 10 to 22 carbon atoms such as a lithium soap of lauric, myristic,palmitic or stearic acid, preferably myristic or stearic acid;

3. from 0.01 to 5.0 percent of a polyether;

4. a base such as lithium hydroxide in an amount sufficient to maintainthe grease on the alkaline side.

The fluid methylpolysiloxanes employed in the practice of the presentinvention are well known in the art. These fluids are describedgenerally in US. Pat. Nos. 2,469,888 and 2,469,890 Patnode. This type ofmethylpolysiloxane can be characterized as having the average unitformula:

where n has a value of from 2.002 to 2.2. Although anymethylpolysiloxane fluid within the scope of formula l is applicable inthe process of the present invention, it is preferred that the fluidhave a viscosity of from about 10 centistokes to about 100,000centistokes when measured at 25 C.

It should be understood that methylpolysiloxane fluids of formula I) caninclude siloxane units of varied types and formulation such astrimethylsiloxane units and dimethylsiloxane units alone or incombination with monomethylsiloxane units. The only requirement is thatthe ratio of the various siloxane units employed be selected so that theaverage composition of the copolymeric fluid is within the scope offormula l One component of the grease compositions of the presentinvention is the grease-thickening agents which are well known in theart. This invention contemplates the use of the lithium soaps of any ofthe higher fatty acids having from 10 to 22 noncarboxyl carbon atoms toform a grease composition of the desired consistency. The term grease asemployed in the present application is intended to refer to greaselikematerials which may have consistencies varying from readily flowablematerials to materials which exhibit essentially no flow. Theconsistency of the greases of the present invention depend on the amountof thickening agent employed, the particular thickening agent employedand the particular polysiloxane fluids in the grease. Examples ofsuitable thickening agents include the lithium soaps of higher fattyacids of 10 to 22 noncarboxyl carbon atoms such as lauric, myristic,palmitic, stearic, and preferably the myristic and stearic soaps oflithium.

While, as explained above, the amounts of thickening agent employed inthe grease compositions of the present invention are not critical andmay vary within wide limits depending on the particular consistencydesired in the final product, it has been found that the amount ofthickening agent usually varies from about 2 percent to 35 percent andpreferably from about 5 percent to 25 percent by weight based on theweight of the grease composition.

One critical feature, however, of the grease composition of the presentinvention is the amount of the polyether present. For satisfactorydispersion of the thickening agent in the polysiloxane, it has beenfound that the polyether must be present in an amount equal to fromabout 0.0l to 5.0 percent by weight based upon the weight of the grease,and preferably from 0.1 to 2.0 percent by weight. When less than 0.01percent by weight of the polyether is present, it is found that it isvery difficult to disperse the thickening agent into the grease and, inaddition, there is a tendency for a higher bleed of the polysiloxanefluid from the grease composition. When the amount of polyether in thegrease composition is in excess of 5.0 percent by weight, it is foundthat the weight loss of the grease at temperatures in excess of 300 F.is so excessive that the grease is unsuitable for use in manyapplications.

The polyethers which are used herein in combination with thepolysiloxane oils according to this invention are polymeric alkyleneoxides and/or polymeric alkylene glycols, and may be represented by thefollowing formulas:

AO-(C,H, ,O),, ,,(Q), wherein A and B represent radicals selected fromthe class comprising hydrogen, alkyl radicals containing from one to 12carbon atoms, cycloalkyl radicals containing five to seven carbon atomsin the ring, mononuclear and binuclear aryl radicals and mononucleararyl lower alkyl radicals wherein the alkyl groups attached to thearomatic nucleus contain a total of no more than five carbon atoms; Aand B also represent ester-forming groups containing from two to 12carbon atoms", A and B may or may not be alike. When there is more thanone A radical per molecule, the A radicals may or may not be the same. Qis a residue of a polyhydric initiator radical containing at least twohydroxyl radicals such as ethylene glycol, glycerol,

trimethylolpropane, and other polyhydric alcohols having from two to sixhydroxyl groups; it is a number having a value of 2 to 4; n is a numberhaving a value of from 4 to 2,000, y has a value offrom 2 to and z has avalue of l to 5.

More specifically, A and B represent radicals selected from the classcomprising hydrogen; alkyl radicals having from one to 12 carbon atoms,e.g., methyl, ethyl, propyl, butyl, octyl, etc. radicals; cycloalkylradicals having five to seven carbon atoms in the ring, e.g.,cyclopentyl, cyclohexyl, cycloheptyl, etc. radicals; mononuclear andbinuclear aryl radicals, e.g., phenyl, naphthyl, biphenyl, etc.radicals; mononuclear aryl lower alkyl radicals wherein the alkyl groupsattached to the aromatic nucleus contain a total of no more than fivecarbon atoms, e.g., benzyl, phenylethyl, phenylpropyl, etc.; and estergroups having from one to 12 carbon atoms such as the residues formed bythe removal of a carboxyl hydrogen from a fatty acid, e.g., an acetate,propionate, octoate, etc.; hydroxyether groups derived from glycols suchas butylene glycol, octylene glycol, etc.; and groups formed byesterification with a hydroxyl group of a nonfatty acid, e.g., propylphosphate, octyl sulfonate, butyl sulfate, etc.

The polyethers may be prepared from the various alkylene oxides (e.g.,ethylene oxide), the higher 1,2-epoxides (such as 1,2-propylene oxide),the alkylene glycols (e.g., ethylene glycol) and mixtures of these. Theresulting products may be polyoxalkylene diols or polyalkylene glycolderivatives; that is, the terminal hydroxyl groups can remain as such,or one or both of the terminal hydroxyl groups can be removed during thepolymerization reaction or subsequent thereto, as by etheriflcation oresterification to yield monoor di-ether or monoor di-ester groups or acombination of such terminal groups whereby certain desirable propertiesare imparted to the final polymeric mixtures. For example, in the aboveformula A and/or B may be: alkyl radicals, forming a di-alkyl polyether(e.g., dibutyl heptaoxypropylene diether); ester forming radicals,forming alkyl oxyalltylene esters (e.g., butyl pentaoxypropyleneacetate); hydrogen, forming polyglycols (e.g., polyethylene glycol),etc.

To further exemplify the polyethers which can be used, the polyetheroil, that is, the Cx(H O)n section of the above formula, can be derivedfrom such basic units as the following oxides:

CH3 sec-propylene oxide (CH,HO)- I sec-butylene oxide (OH,OHO)

CH tert-butylene oxide -(CH,( JO). etc.

or basic units obtained by the dehydration of alkylene glycols,resulting in the formation of the following:

ethylene oxide -(CH CH,O)-, propylene oxide (CH CH -CH O)-, butyleneoxide -(Cl-l CH Cl-l -CH O), etc.

Polyethers containing combinations of the above-described basic unitshave been found to be quite useful in the practice I The molecularweight of the polyether oils used according to this invention can rangefrom 300 to 200,000; from 400 to 20,000 being preferred.

In addition to the above-described components, additives normallypresent in silicone greases can be present in the composition of thepresent invention. Examples of additives include antioxidants such asthe amines, e.g., N-phenyl-alphanaphthyl amine; corrosion inhibitors,e.g., zinc naphthanate; and extreme pressure additives such as seleniumdisulfide, molybdenum disulfide, etc.

There are a number of methods for forming the compositions of thepresent invention. In the preferred method, the polysiloxane fluid, thelithium soap-thickening agent, the polyether dispersing agent and asmall amount of a finely ground base such as lithium hydroxide areheated to a temperature of about 400 to 500 F. after which the greasecomposition is cooled to room temperature, then milled.

The following examples are illustrative of the practice of the presentinvention and are not intended for purposes of limitation.

EXAMPLE 1 In this example a grease composition was prepared employing atrimethylsilyl chain-stopped polydimethylsiloxane having a viscosity of350 centistokes when measured at 25 C. as a base fluid. To 540 grams oflithium myristate and 30 grams of a polyoxalkylene polyol of theformula:

were added 1,080 grams of the base fluid and 0.9 grams of finely dividedlithium hydroxide. The components were thoroughly mixed and then heatedto 470 F. The mixture was slowly cooled l.4 F. per minute) to 345 F. atwhich point 15 grams of N-phenyl-alpha-naphthylamine and 1,365 grams ofthe base oil were added with continuous stirring. The slow cooling wascontinued and at 210 F. 1.5 gram of finely divided lithium hydroxide wasadded and the grease was cooled to room temperature still withcontinuous stirring. The grease formed was milled through a Morehousemill three times. Processing was very smooth and very few lumps wereformed due to the lithium myristate conglomerating during mixing.

A comparison grease was formed to determine the efiect of the additionof the polyether on the ease of processing. The grease was prepared inexactly the same manner as that prepared earlier in the example exceptthat no polyether was added. The processing was very difficult due tothe formation of lithium myristate lumps during the mixing operation.The lumps would not pass through the mill with the rest of theingredients. A comparison of the two greases showed that the greasecontaining the polyether was a thicker, smoother grease and there wasmuch less tendency for the silicone oil to separate from the grease.

EXAMPLE 2 To 540 grams of a mixture containing 60 percent of lithiumstearate and 40 percent of lithium palmitate were mixed 1,080 grams ofthe base oil described in example 1, 0.9 grams of lithium hydroxidewhich had been preground on a three roll mill with a small portion ofthe lithium stearate-lithium palmitate-base oil mixture and then withcontinued stirring was added 30 grams of a polyoxyalkylene polyol of theformula:

The mixture was heated to 475 F. with continued stirring. The mixturewas then slowly cooled (l.4 F. per minute) to 345 F. at which point 15grams of N-phenyl-alphanaphthylamine and 1,365 grams of the base oilwere added, still with continued stirring. The slow cooling wascontinued and at 212 F. an additional 1.5 grams of lithium hydroxide,which had been preground as described above, was added and the greaseformed was cooled to room temperature, still with continuous stirring.The grease formed was milled through a Morehouse mill three times.Processing was very smooth and few lumps were present due to lithiumsoap conglomerating.

For comparison purposes a grease identical in all respects except thatthe polyoxyalkylene polyol was omitted from the formulation. Theprocessing of the comparison grease was very difficult and the greasewas quite lumpy upon completion of the mixing operation due to theconglomeration of particles of lithium stearate and palmitate. Many ofthe larger, harder lumps remained in the mill reservoir, resulting in athinner grease. The grease produced containing the polyoxyalkylenepolyol was much less prone to bleeding than the comparison greaseespecially at high temperatures.

EXAMPLE 3 In this example a grease composition was prepared employing atrimethylsilyl chain-stopped polydimethylsiloxane having a viscosity of100 centistokes when measured at 25 C. as a base fluid. To 540 grams oflithium myristate and 30 grams of polyoxyalkylene polyol of the formula:

were added 1,080 grams of the base fluid and 0.9 grams of finely dividedlithium hydroxide. The components were thoroughly mixed and then heatedto 470 F. The mixture was slowly cooled l.4 F. per minute) to 345 F. atwhich point 15 grams of N-phenyl-alpha-naphthylamine and 1,365 grams ofthe base oil were added with continuous stirring. The slow cooling wascontinued and at 210 F. 1.5 gram of finely divided lithium hydroxide wasadded and the grease was cooled to room temperature still withcontinuous stirring. The grease formed was milled through a Morehousemill three times. Processing was very smooth and very few lumps wereformed due to the lithium myristate conglomerating during mixing. Acomparison grease was formed to determine the effect of the addition ofthe polyether on the ease of processing. The grease was prepared inexactly the same manner as that prepared earlier in the example exceptthat no polyether was added. The processing was very difficult due tothe formation of lithium myristate lumps during mixing. A comparison ofthe two greases showed that the grease containing the polyether wasthick and smooth whereas the comparison grease was thinner and the millreservoir had little round balls like buckshot in it, formed from thelithium myristate. The balls would not pass through the mill. The ballswere so hard that a treatment more severe than that conventionally usedwould be required to break them up.

EXAMPLE 4 In this example a grease composition was prepared employing atrimethylsilyl chain-stopped polydimethylsiloxane having a viscosity of350 centistokes, when measured at 25 C. as a base fluid. To 560 grams oflithium myristate and 31.2 grams of a polyether of the fonnula:

were added 1,200 grams of the base fluid and 1.0 grams of finely dividedlithium hydroxide. The components were thoroughly mixed and then heatedto 470 F. The mixture was slowly cooled 1.4 F. per minute) to 345 F. atwhich point 20 grams of N-phenyl-alpha-naphthylamine and 1,740 grams ofthe base oil were added with continuous stirring. The slow cooling wascontinued and at 210 F. 1.0 gram of finely divided lithium hydroxide and440 grams of lithium myristate were added and the grease was cooled toroom temperature still with continuous stirring. The grease formed wasmilled through a Morehouse mill three times. Processing was very smoothas there were very few lumps fonned due to the lithium myristateconglomerating during mixing.

A comparison grease was formed to determine the effect of the additionof the polyether on the ease of processing. The grease was prepared inexactly the same manner as that prepared earlier in the example exceptthat no polyether was added. The milling was very difficult due to thepresence of lithium myristate lumps which had formed earlier in theprocess clogging the inlet to the mill. A comparison of the two greasesshowed that the grease containing the polyether was a thicker, smoothergrease and there was much less tendency for the silicone oil to separatefrom the lithium myristate especially at high temperature. Thecomparison grease was deficient in soap due to the impossibility ofgetting many of the larger soap lumps through the mill. The greasecontaining the polyether had the following properties:

While the foregoing examples have illustrated certain embodiments of thepresent invention, it should be understood that our invention is broadlyapplicable to grease compositions containing polysiloxanes, thesubstituents of which are all methyl groups in combination with alithium soap of a higher fatty acid, from 0.01 to 5.0 percent of apolyether and a sufficient amount of base to maintain the composition onthe alkaline side.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A grease composition consisting essentially of on a weight basis:

1. from about 61 percent to about 98 percent by weight based upon theweight of the grease of a fluid methyl polysiloxane having a viscosityof from about 10 to about 100,000 centistokes having the average unitformula:

where n has a value of from 2.002 to 2.2;

2. from about 2 percent to about 35 percent by weight based upon theweight of the grease of a grease-thickening lithium soap of a fatty acidhaving from 10 to 22 noncarboxyl carbon atoms;

3. from 0.01 percent to 5.0 percent by weight based upon the weight ofthe grease of a polyether selected from the group consisting of whereinA and B represent radicals selected from the class consisting ofhydrogen, alkyl radicals containing one to 12 carbon atoms, cycloalkylradicals containing five to seven carbon atoms in the ring, mononuclearand binuclear aryl radicals and mononuclear aryl lower alkyl radicalswherein the alkyl groups attached to the aromatic nucleus contain atotal of no more than five carbon atoms; Q is a residue of a polyhydricinitiator radical containing at least two hydroxyl radicals selectedfrom the class consisting of ethylene glycol, glycerol,trimethylolpropane, and other polyhydric alcohols having from 2 to 6hydroxyl groups; n is a number having a value of from 4 to 2,000; x is anumber having a value of 2 to 4; y has a value of from 2 to 10; and 2has a value of from 1 to 5; the polyether having a molecular weight offrom about 300 to about 200,000;

4. a metal base in an amount sufiicient to maintain the side is lithiumhydroxide. 3. The grease composition of claim 1, wherein thegreasethickening lithium soap is lithium myristate.

4. The grease composition of claim 1, wherein the polyether is presentin an amount constituting from 0.! percent to 2.0 percent of the greasecomposition.

It I I I l

2. The grease composition of claim 1, wherein:
 2. the polyether ispresent in an amount constituting from 0.1 to 2.0 percent by weight ofthe grease composition;
 2. from about 2 to about 35 percent by weightbased upon the weight of the grease of a grease-thickening lithium soapof a fatty acid having from 10 to 22 noncarboxyl carbon atoms;
 3. from0.01 to 5.0 percent by weight based upon the weight of the grease of apolyether selected from the group consisting of A-O-(CxH2x0)n-B and(A-O-(CxH2xn)y(Q)z wherein A and B represent radicals selected froM theclass consisting of hydrogen, alkyl radicals containing one to 12 carbonatoms, cycloalkyl radicals containing five to seven carbon atoms in thering, mononuclear and binuclear aryl radicals and mononuclear aryl loweralkyl radicals wherein the alkyl groups attached to the aromatic nucleuscontain a total of no more than five carbon atoms; Q is a residue of apolyhydric initiator radical containing at least two hydroxyl radicalsselected from the class consisting of ethylene glycol, glycerol,trimethylolpropane, and other polyhydric alcohols having from 2 to 6hydroxyl groups; n is a number having a value of from 4 to 2,000; x is anumber having a value of 2 to 4; y has a value of from 2 to 10; and zhas a value of from 1 to 5; the polyether having a molecular weight offrom about 300 to about 200,000;
 3. the metal base used to maintain thegrease on the alkaline side is lithium hydroxide.
 3. The greasecomposition of claim 1, wherein the grease-thickening lithium soap islithium myristate.
 4. The grease composition of claim 1, wherein thepolyether is present in an amount constituting from 0.1 to 2.0 percentof the grease composition.
 4. a metal base in an amount sufficient tomaintain the grease on the alkaline side.